How do I attach these arms to the torso?
You already did all the important steps. All you have left to do is move the arm into place (you could use snapping). After the arm is aligned, simply remove doubles.
W > Remove Doubles, from the 3D view header > Mesh > Clean Up > Remove Doubles, or from the tool shelf, tools tab Remove Doubles.



If you did not have every vertex perfectly aligned. You could select both the loop on the arm and the loop on the shoulder and Bridge Edge Loops.
Or you could go around selecting each vertex and its corresponding pair on the shoulder and Merge the vertices M > At Center, or from the 3D view header > Mesh > Vertices > Merge > At Center.

Three ways to do this, all pretty easy.